Transmissions featuring floating transmission mainshaft gears such as associated with twin countershaft transmissions are well known and examples of which can be found in U.S. Pat. Nos. 3,237,472; 3,238,613; 3,425,290; and 3,885,446, the disclosures of which are incorporated herein by reference.
Such transmissions generally feature a plurality of floating mainshaft gears that encircle the mainshaft and are supported and driven by countershaft gears, typically countershaft gears, that are respectively mounted on a pair of countershafts disposed on opposite sides of the mainshaft.
The mainshaft gears are characteristically clutched to the mainshaft by means of a clutch mechanism that slides along external splines extending axially along the mainshaft and has radially inwardly extending teeth or splines that engage internal teeth or splines on the mainshaft gear so as to cause rotation of the mainshaft when the mainshaft gear is clutched thereto.
A problem long ago recognized has been the potential transfer of axial thrust to a mainshaft gear being clutched to the mainshaft causing it to move axially which is of particular concern in view of mainshaft gears that are in close proximity to each other. In view of such, a variety of solutions have been devised over past years for the transmitting axial thrust imparted by an axially moving clutch to the mainshaft rather than to the gear being clutched to the mainshaft.
Such solutions have generally been in the form of gear retainer(s) of one type or another that characteristically limit axial movement of the mainshaft gear of which one example is disclosed in U.S. Pat. No. 2,397,905, the disclosure of which is incorporated herein by reference. Here however, a costly and expensive pivotal Woodruff key is required to lock a thrust collar onto external splines of the mainshaft to prevent a gear from moving axially.
An example of a splined thrust washer for transmitting axial thrust from a gear set to a propeller drive shaft is disclosed in U.S. Pat. No. 3,894,621, the disclosure of which is incorporated herein by reference. Here, a splined thrust washer (52) is slid axially along the shaft splines to a transverse groove adjacent a stepped shoulder on the shaft and is held in place against the shoulder by a splined collar (30). Thrust washer (52) is operative to transmit axial thrust of only one gear to the propeller shaft and, in addition to requiring the use of collar (30), also requires costly and complex machining of a stepped configuration to the propeller shaft exterior.
Another example of a transmission mainshaft gear retainer for preventing axial movement of two closely spaced gears to prevent transfer of axial thrust force therebetween is disclosed in U.S. Pat. No. 4,034,620, the disclosure of which is incorporated herein by reference. Here a thrust ring (104) is splined to the mainshaft between two adjacent gears and is held in place by means of snap rings (108, 110) on opposite sides thereof. The gears are further required to have costly and complex mating tongue and groove configurations that operate in conjunction with an additional snap ring (102) to limit movement of the gears away from each other.
Another example of thrust devices for use in transmitting thrust from a floating mainshaft gear being clutched to a mainshaft is described in U.S. Pat. No. 4,104,928, the disclosure of which is incorporated herein by reference. However, it is not clear precisely what construction is used to prevent closely adjacent gears from contacting each other during the clutching process.
Yet another example of a gear retainer for preventing closely adjacent mainshaft gears from contacting each other while one is being clutched to the mainshaft is described in U.S. Pat. No. 4,485,686, the disclosure of which is incorporated herein by reference. Here, however, two snap rings (82) and (96) are required in addition to having to provide the inner periphery of thrust plates (86) and (92) with splines (86) and (98) respectively in order to enable the mainshaft to rotate the thrust plates while holding them against a common spacer (90) located between the two thrust plates.
A somewhat similar thrust plate arrangement to that disclosed in above described U.S. Pat. No. 4,485,686 is described in U.S. Pat. No. 4,423,643.
A more recent example of a three thrust plate arrangement in conjunction with providing closely adjacent mainshaft gears (30) and (32) with flanges having thrust surfaces on opposite sides is disclosed in U.S. Pat. No. 4,949,589 owned by the assignee of the present invention and the disclosure of which is incorporated herein by reference.
Although the above described thrust plate or gear retainer arrangements may be effective, they heretofore have been characteristically complex in their construction and number of parts creating a need to provide a simpler means for transmitting axial thrust to a mainshaft imparted by a clutch to a floating mainshaft gear being clutched to the mainshaft.